8:45 The first plane hit the North Tower.
9:03 The second plane hit the South Tower.
10:05 The South Tower collapsed.
10:28 The North Tower collapsed.
Even after the planes hit the buildings, who could foresee that the South Tower would collapse before the first-hit North Tower? Who would know that the towers would collapse at all? I read that the engineering designs for the towers said that the towers could take the impact of a jet plane. What they hadn't considered was the fact that the planes would be loaded with jet fuel. (Only in engineering do planes fly without fuel.)
You forgot to include,
5:20pm WTC 7 collapsed. (no plane hit this building)
Structural Engineers don't consider fire risk to a buildings collapse if the building is a steel truss framed building simply because most fires would not be hot enough to weaken the steel truss frame to the point whereby it would make it collapse under its own weight. To have 3 high rise steel truss frame building collapse on a single day to fire would have been highly statistically unlikely. Even more so within an hour of the steel frames being heated by a moderately cool fire such as happened within WTC1, WTC2 and WTC7. These buildings had very large multiple safety factors (they are over engineered) inherent in their designs where they had to withstand huge wind shear forces (velocities greater than a Cat 3-4 Hurricane - the designers were aware of the Long Island Express) which were many times greater than the strength required to withstand the gravitational forces of the buildings own weight even if all the structural steel had suddenly lost half its tensile strength when structural steel is heated to beyond 600 degrees Celsius (not just a few floors). It also take a long time (many hours) to heat hundreds to thousands of tonnes of structural steel to these temperatures due to the specific heat properties of structural steel.
A steel frame building will begin to sag and buckle before it collapses from the effects of fire as described here;
http://www.sheilacasey.com/2008/06/windsor-fire-in-madrid-vs-wtc-fires-on-911.html 
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